import { pure, fail, anyItem, satisfy, literal, parse, parseSome, ParseError, EofError } from '../src/parser.js'
import { Err, Result } from '../src/result.js'
import { describe, it } from 'node:test'
import assert from 'node:assert/strict'

const eq = (a, b) => assert.deepStrictEqual(a, b)
const parseErr = (i, desc) => new Err(new ParseError(i, desc))
const eof = (i = 0) => new Err(new EofError(i))

const streamState = stream => {
  return [stream.index, Array.from(stream.clone())]
}

describe('Primitive parsers', () => {
  it('pure', () => {
    const result = parseSome(pure(123), 'abc')
    const [value, stream] = result.unwrap()

    eq(value, 123)
    eq(streamState(stream), [0, ['a', 'b', 'c']])

    const empty = parse(pure(123), [])
    eq(empty, Result.ok(123))
  })

  it('fail', () => {
    const msg = 'Expected failure'
    const parser = fail(msg)
    const expected = parseErr(0, msg)

    eq(parse(parser, 'abc'), expected)
    eq(parse(parser, ''), expected)
  })

  it('anyItem', () => {
    const parser = anyItem()
    eq(parse(parser, 'a'), Result.ok('a'))

    const many = parseSome(parser, 'abc')
    assert(many.isOk())
    const [value, rest] = many.unwrap()

    eq(value, 'a')
    eq(streamState(rest), [1, ['b', 'c']])

    eq(parse(parser, ''), eof())
  })

  it('satisfy', () => {
    const pa = satisfy(x => x === 'a')

    const result = parseSome(pa, 'abc')
    assert(result.isOk())

    const [value, rest] = result.unwrap()

    eq(value, 'a')
    eq(streamState(rest), [1, ['b', 'c']])

    const err = parse(pa, 'cba')
    eq(err, parseErr(0, 'Value did not match predicate: c'))

    const eofErr = parse(pa, '')
    eq(eofErr, eof())
  })

  it('literal', () => {
    const px = literal('x')
    const result = parseSome(px, 'xyz')
    assert(result.isOk())

    const [value, rest] = result.unwrap()
    eq(value, 'x')
    eq(streamState(rest), [1, ['y', 'z']])

    const err = parse(px, 'yz')
    eq(err, parseErr(0, 'Value did not match predicate: y'))

    const eofErr = parse(px, '')
    eq(eofErr, eof())
  })
})